Electric discharge tube



April 2, 1940. c. H. BACHMAN ELECTRIC DISCHARGE TUBE Filed Sept. 22, 1937 2 Sheets-Sheet 1 AAAAAAA INVENTOR ATTORN EY ATE.

April 2, 1940. c. H. BACHMAN ELECTRIC DISCHARGE TUBE Filed Sept'. 22, 1937 2 Sheets-Sheet 2 T WE.

lNVENTOR BY 7M ATTORN EY Patented Apr. 2, 1940 ELECTRIC DISCHARGE TUBE Charles H. Bachman, St. Marys, Pa., assigner to Hygrade Sylvania Corporation,

Salem,

Mass., a, corporation of Massachusetts Application September 22, 1937, Serial No. 165,037

Claims.

This invention relates to electric discharge tubes and more especially to discharge tubes of the type employing a conductive iilling of an ionizable medium such as gas or vapor or a mix- .,3, ture thereof.

A principal object of the invention isy to provide an improved gaseous conduction tube which is especially useful as a voltage regulator.

Another principal object is to provide an imu) proved gaseous conduction tube which is especially useful vas a Voltage divider.

Another object is to provide an improved form of multi-section gaseous conduction tube. V

A feature of the invention relates to a gasir.. eous conduction tube of the type employing a plurality of cathodes, all having uniform normal cathode drop over the discharge surface.

A further feature relates to a gaseous conduction tube of the multi-section type having the electrodes arranged to have uniform` normal cathode drop over all the cathode surfaces, and with any predetermined ratio of maximum currents to be carried by the several sections; and more especially to an arrangement wherein a u one-to-one current carrying ratio 4is desired for the several sections.

Another feature relates to an electric discharge tube of the type having a plurality of separate discharge chambers wherein 4 the intro- 30 duction of impurities is materially reduced by avoiding not onlythe use of relatively large ceramic spacers or supports for the electrodes but also large ceramic-coated surfaces.

A further feature relates to a gaseous dis- 35 charge 'tube having an electrode arrangement which may be duplicated for two or more discharge sections with uniformity of active-coated area and uniformity of cathode drop for all sections, thus enabling a single tube to contain a number of independent voltage dividing or voltage regulating units. y

A still further 'feature relates to the novel organization, arrangement and relative location of parts which constitute a simple, efficient and 45 improved voltage regulator tube of the gaseous conduction type.

f While the invention will be illustrated herein as embodied in certain specic structures, proportions and arrangement of parts, it will be 50y understood that this is done merely for explanatory purposes and not by way of limitation. Accordingly, in the drawings:

Fig. 1 `shows typical characteristic curves of gaseous conduction tubes.

5m Fig. 2 shows a typical circuit embodying a the electrodes of Fig. 5`. 10

Figs. '7, 8 and 9 represent, respectively, three different ways of protecting the lead-in wires and isolating the several discharge chambers.

Referring to Fig. 1, the curve I represents the voltage-current characteristic of a glow-dis- 15 charge tube suitable for use as a Voltage regulator or voltage divider. Curve II is another typical characteristic curve of a glow-discharge tube.I In Fig. 1, the abscissae represent the current flow between the electrodes through the gaseous filling and the ordinates represent the voltage across the electrodes. In curve I it will be noted, that' between the voltages V1 and Vz the characteristic curve is substantially flat and is nearly parallel to the current axis over a substantial range of current Values between i1 and i2. The nearly constant voltage drop Vn in this region is practically equal to the normal cathode drop at the cathode in a given gas filling. In order to obtain a characteristic with a substantially flat region such as that shown in curve I, certain conditions have to be fulfilled as to the geometry of the tube, the gas filling and pressure, cathode material and surface. The flat region of the characteristic curve corresponds to an increase in total current for constant current density at the cathode. Such an increase in'total current at constant current density and constant cathode drop requires that the cathode drop shall not vary as the discharge spreads over larger areas of the cathode surface. If a variation of the cathode drop exists, the characteristic curve of the dischargey tube may be of the general shape of curve II. With such a characteristic, the voltage drop of the discharge varies considerably between current values i1 and i2. Since the region of curve II between the points V4 and V5 is not parallel to the current axis, a tube with a characteristic similar to curve II would therefore be a relatively poor voltage regulator for current values between i1 and i2. While a tube having a characteristic such as that of curve II may be used over the current region i3 to iz, it would require an appropriate voltage drop resistor in series with the load. 55,

Cil

In any event', the desirable characteristic of a voltage regulator tube of the glow-discharge type is the one represented by curve of l and thus, one of the principal objects of the invention is to correlate the various parts to insure this kind of characteristic curve, so that the cathode drop is uniiorin. for all sections of a multi-section tube.

Fig. 2 represents in schematic form a typical circuit wherein a glow-discharge tube may be used as a voltage regulator. Terminals T1 and T2 represent a source of supply potential, and numeral 3 represents any suitable form of load to be operated at a substantially constant potential. For this purpose there is connected across supply terminals T1 T2, a glow-discharge device consisting or" an enclosing envelope fi containing a. iilling of an ionizable medium such as an inert or noble gas or mixture of such gases at the proper pressure to provide a glow-discharge between the cathode l and the anode 2 preferably with the anode area very much smaller than the cathode area. A current limiting resistance R is coni, cted in series with the glow-discharge device across the supply terminals. If the glow-discharge device has a peaked characteristic such as that of curve II (Fig. l), it is necessary to employ a separate resistor r in series with the load device Regulator tubes of the glow-discharge type with a low voltage drop, for example ci the order of 90 volts, are generally filled with one noble gas or a mixture of noble gases at a pressure, adapted to the geometry of the tube, of the order of about l min. of mercury. The cathodes of such tubes may be provided with materials for reducing the cathode drop. As examples of the coating materials usually employed may be mentioned pastos formed of the oxides and carbonatos and solutions of the nitrates of the alkaline earth metals. The break-down temperatures of such pastos are rather critical, and it is very important that a uniform temperature be applied to all the cathodes during the break-down process.

Different methods may be used to heat the cathodes for this break-down purpose, for example the electrodes may be heated by either a D. C. or an A. C. gas discharge, or they may be heated by the wellknown induction heating process such as is customarily employed in the bombardment processing of radio tubes. I have found that in general where the break-down temperature is attained by a `gaseous discharge process that the temperature over the cathode surface will not be uniform. However in the case of induction heating, the temperature can be easily controlled and kept constant if the electrodes to be heated are approximately cylindrical in shape. While the problem 0f designing a single section glow-discharge tube with a cylindrical cathode surface capable of being heated inductively in a uniform manner, is relatively simple, the same is not true where the tube is to contain a plurality of discharge sections each oi which is to be independent, so far as its discharge is concerned, from the remaining sections. ln other words, where a plurality of sections are utilized the electrodes must be so arranged that the heating effect of the high frequency induction field is substantially the same for all cathodes.

Fig. 3 shows in cross section one known structure of a two-section glow-discharge voltage regulating tube. The electrodes 5, S and 'I are in the form of nested cups with their lips seated in circular grooves in the ceramic disc-shaped insulator 8 by means of which they are spaced concentrally and insulated electrically. A suitable ceramic paste S is employed to attach the electrodes to the ceramic discs and to separate the two interelectrode discharge spaces from each other. Thus the discharge spaces are separated partly the electrode themselves and partly by the ring-shaped surface of the insulate; disc between the grooves and a considerable surface extent of ceramic paste is exposed in each discharge space. The leads I0, Il and l2 are insulated froin one another and are brought out through respective holes in the ceramic disc 8 to the stem oi the tube (not shown). With the construction of Fig. 3, it will be noted that the inner electrodes and E are shielded against induction heating by the outer electrode l, thus preventing the development of a uniform temperature in all the cathodes when they are outgassed, and when the cathode coating is broken down by induction heating. Furthermore, the large exposure of ceramic surface to the discharge spaces introduces undesirable impurities when heated. ilurthermore because of the relatively heavy of the ceramic 8, the portions of each electrode adjacent this ceramic are not heated to the same degree as the remote portions because oi' the relatively large heat capacity of the ceramic. In addition, this construction requires that successive electrodes be of successively greater' surace extent. Consequently the maxicurrent capacity of the inner cathodes at normal cathode drop is smaller than that of the outer cathode, in the ratio of the surfaces of the cathodes.

ln order to overcome the above-noted and other disadvantages, there is shown in Fig. 4 a multisection glow-discharge tube comprising an enclosing envelope I3 oi glass or other suitable material provided with a reentrant stem |3a terminating in a conventional press 2Q. If desired the upper end of the envelope may be provided with a dome 21, as the blanks known as ST- bulbs. Sealed into the press 25, preferably concentrally thereof, is a rod or wire I4 of a suitable metal such as iron, nickel, molybdenum and the like. While the drawings show the rod I4 of a single piece, it will be understood that the portion passing through the press 2U, may be of a different metal or alloy having substantially the same coeilicient of expansion as the glass of the press. The rod i4 is designed to act as the iinal anode of the tube. While Fig. 4 shows a double section tube, the principle of the structure may however, be applied to tubes with more than two sections without deviating from the scope ci the present invention. The cathode which cooperates with the anode I4 consists of a metal cylinder l5 having its lower end provided with an annular metal disc I5a joined to a cylindrical extension i6. The upper end of electrode l5 is completely closed by the metal disc lb. It will be understood of course that the parts l5, a and i6 instead of being made in separate pieces integrally joined, may be formed as a single unit from a suitable metal blank. The member I6 acts as the anode for the cooperating cathode l1, which consists of a metal cylinder preferably, although not necessarily, of the same diameter as electrode I5. The upper end ci electrode ll is closed olf by means of a disc i9?) preferably of mica or similar material, disc 19h being provided with a central circular opening through which passes anode I6. Preferably, although not necessarily, another disc I9a of mica or similar material similar to disc I8b is provided for purposes to be described.

In order to protect the electrode I4 from discharging to electrode I1, there is provided a cylindrical glass tube or collar 2I surrounding the said electrode I4, said collar if desired being formed integrally with the press 20. The electrode structure or mount is supported from the press by means of wires I8, I8a which are welded to the outer face of electrode I1, and the upper ends of wires I8, Illa may be off-set where they pass through the mica disc I9b. Disc I9b may be fastened in place to the wires I8, I8a in any wellknown manner, for example the said disc may be provided with metal eyelets I9c to which the wires I8, I8a are welded or otherwise fastened, the electrode I5 being protected from a direct discharge to the eyelets I9c or wires I8, I8a by the mica disc I9a. For the purpose of preventing lateral tilting movement of the mount, there is provided a mica disc I9 which rests against the top I5b of electrode I5. Disc I9 may be held in place by metal tabs or extensions I8c carried by the electrode I5. Disc I8 may be provided on its periphery with flexible teeth or extensions to engage the dome 21, thus providing a shock-proof support for the upper end of the mount. The lead wire 23 extends through press 20 and is connected to the electrode I6, but instead of kconnecting leadwire 23 to electrode I6, the said lead-wire may extend vertically through aligned holes in the discs |90., I9?) to contact with'the portion I5a of electrode I5.

From the foregoing arrangement, it will be seen that the lower discharge section of the tube comprises the cathode I1 and the portion of member I6 which extends downwardly below the disc I9b, while the upper discharge section comprises the cathode I5 and the anode I4. It will be understood that the extension I6 i'lts tightly in the opening in disc I9b so as to isolate effectively the two discharge spaces.

The parts are preferably so proportioned that the active area of cathode I 5 is substantially the same as the active area of cathode I1, it being understood that the inner active faces of both cathodes are provided with a coating of one of the pastes mentioned hereinabove. For example pastes of the oxides and carbonates of the alkaline earth metals; it being understood of course that any other wellknown material for reducing the cathode drop may be employed. After the various electrodes have been assembled on the press, the envelope is highly evacuated in any wellknown manner and is thereafter provided with a filling comprising one or more of the noble gases, or a mixture of such gases with a metallic vapor, and preferably so proportioned that the pressure of the inert gas is approximately 10 mm. of mercury. After the tube has been evacuated, the cathode coating material is broken down by positioning a high frequency heating coil around the envelope I3 preferably with the axis of the coil concentric with the electrodes I4 and I1 and the said electrodes are brought to the temperature necessary to break down the coating material thereon.

From the foregoing description, it will be seen that because of the concentric superposed relation of the cathodes, they can readily be heated to substantially the same temperature by the conventional high frequency induction heating coil. Secondly the introduction of impurities and the cross section of possible paths leakage between the electrodes are materially reduced, because of the absence of heavy ceramic bodies between the electrodes. Finally, the number of discharge sections may be increased within reasonable limits,

the cathode areas of all the sections being either equal or the areas of consecutive cathode sections having a desired ratio.

Fig. 5 shows a modification of the electrode arrangement of Fig. 4. In this embodiment, there is shown a mount for a glow-discharge voltage regulator tube having two distinct discharge sections. The electrodes of each section are designated 33, 34 and 35 respectively and each electrode is in the form of a shallow cup having a downwardly depending rim 46. The electrodesy are mounted and held in vertical spaced relation by means of a mica cylinder 36 formed from sheet mica or the like. Each electrode is held in place by a corresponding wire band or loop 45 which is tightened just enough to buckle the mica sheet slightly, forcing it into a corresponding circumferential groove in the associated rim 46. In this embodiment the electrode 34 acts not only as the anode to the associated cathode 33 which has its surface coated as above-mentioned, but also as a cathode to the associated anode 35. For the latter purpose the upper face of electrode 34 is provided with a coating of the materials mentioned hereinabove for reducing the cathode dropincluding, for example, pastes of the oxides and carbonates of the alkaline earth metals.

The mount is supported vertically by means of metal tabs or wire 32 which may be Welded to the electrode 33 at their upper vends and sealed at their lower ends into the press 3I. Lead wires 4D, 4I and 42 are likewise sealed into the press 32 and are connected respectively to the electrodes 33, 34 and 35. Press 3l is also preferably provided with upwardly extending glass tubes 31, 31a, which surround respectively the wires 4I andk 42. The tubes 31, 31a fit tightly 'within the corresponding opening in the electrodes 33 and 34 respectively, thus completing the discharge sections and separating them in a discharge-tight manner. Preferably the upper surface of electrode 35 is protected against discharge by means of a mica disc 36a which may be held in place thereon in any wellknown manner. Preferably also, the mica cylinder 36 extends upwardly for an appreciable distance beyond the electrode 35 so as to increase the lengths of possible leakage paths. The mount when assembled as above described is positioned Within an enclosing envelope similar for example to envelope I3 (Fig. 4) which is subsequently evacuated and provided with a filling of a suitable ionizable medium for sustaining a glow-discharge. With this'arrangementl the electrodes can be outgassed and the cathode coating material on the upper surface of electrode 33, and the cathode coating material on the upper surface of electrode 34, can be broken down by using the conventional high frequency induction heating coil in the wellknown manner.

If it is desired to increase the active area of the electrodes in the embodiment of Fig. 5, instead of employing cup-.like members having at bottoms, the latter may be made convex as indicated schematically in section in Fig. 6. Other equivalent methods of increasing the surface area of each electrode may be employed, for example the electrodes of Fig. 5 may be provided with circular or spiral corrugatlons or other corrugations for this purpose.

While Figs. 4 and 5 show the lead wires as being protected by glass tubes 2|, 31 and 31a, the necessary tight iit between these tubes and the associated electrodes through which they pass may be achieved by employing an additional ceramic sleeve. Thus as shown in Fig. 7, the Wire 4l corresponding to Wire 4l of Fig. 5, is surrounded by the glass tube 3l' which in turn is surrounded by a thin wall ceramic tube 31C which is inserted into a corresponding hole in the electrode 33 by a press t. Similar ceramic tubes may be provided around the glass tube 31a (Fig. 5) Where the latter passes through the electrodes 33 and 34. Instead of using a single length of glass tubing such as tubing 2l, 31 or 31a, the tubing may be made in two pieces which are adapted to t tightly over an intermediate thin-Walled ceramic tube. Such an arrangement is shown in Fig. 8 wherein the glass tubing 31d instead of extending through the electrode 33 terminates below said electrode and fitted tightly into the upper end of tube 31d is the thin wall ceramic tube 31e which is press-fitted Within the opening in electrode 33. The ceramic tube 31e extends upwardly beyond electrode 33 and is tightly tted within another section of glass tubing 31j.

In the modification of Fig. 9 the lead-in wires, for example lead-in wire 4l instead of being provided with ceramic or glass tubes as in the embodiments of Figs. '7 and 8, is provided with a coating 43 of ceramic material, for example aluminum oxide, in the manner wellknown in the art of insulating heater laments for radio tubes. The gap between the coating 43 and the opening in the electrode through which it passes, for example electrode 33, is closed by a hardened ceramic paste 44 of any well-known composition.

Various changes and modications may be made in the embodiments disclosed Without departing from the spirit and scope of the invention.

What I claim is:

1. An enclosing envelope containing an ionizable medium, a rst tubular cathode, a second tubular cathode, said cathodes being superposed, a tubular extension from the rst cathode extending into the second cathode to act as an anode for said second cathode, means closing said cathodes and forming separate discharge chambers, an anode extending through said tubular extension and into the first cathode and means insulating the last mentioned anode from said second cathode.

2. A device according to claim 1 in which the last mentioned anode, the cathodes and said tubular extension are substantially co-axial.

3. An enclosing envelope containing an inert gas for sustaining an electric discharge, a tubular cathode, an insulator disc closing off the upper end oi said cathode, said disc having an opening therethrough, a second tubular cathode having a tubular extension extending through the opening in said disc into the first cathode, means closing oi the upper end of the second mentioned cathode, an anode extending through said tubular extension into the second mentioned cathode and means to prevent a discharge between the last mentioned anode and the rst mentioned cathode.

fi. A device according to claim 3 in which the envelope is provided with a press and all of said electrodes are supported by said press.

5. An electric discharge tube for supplying multiple divided voltages from a source of voltage comprising an enclosing envelope having a lling ci an ionisable medium, means defining a plurality of individual discharge gaps within the said envelope, each having discharge sustaining electrodes, one of said electrodes acting as an anode for one gap and as a cathode for another gap, the cathodes of both gaps having substantially the same maximum current capacity for normal cathode drop, one of said cathodes having a reduced neck surrounded by the other cathode but insulated therefrom to act as an anode for said other gap, and lead wires to all the electrodes to apply the divided votages to corresponding points of a load circuit.

CHARLES H. BACHMAN. 

